The purification of water by reverse osmosis is a well known technology which is being used considerably more today than it was in the past due to increasing drinking water problems resulting from pollution, and the like. The increasing usage of this old technology has resulted in the development and refinement of systems which are economically and technically feasible for use in both domestic and industrial applications.
A typical reverse osmosis water purification and storage system currently used for home application employs a special diaphragm-type hydro-pneumatic storage tank into which the purified water from a reverse osmosis unit is stored. The special tank is provided with a diaphragm to divide it into a water storage compartment and a pre-pressurized air compartment. Pure water from the reverse osmosis unit is directed into the water storage compartment and, by diaphragm action, will compress the air in the pre-pressurized air compartment. When a demand for pure water occurs, the compressed air in the air compartment exerts a force on the diaphragm causing the water in the storage compartment of the tank to flow under the influence of that force through a plumbing line to an open fixture, usually a faucet. Systems are also available which employ a tank which stores the purified water at atmospheric pressure. A pump is included in the system to deliver water from the storage tank to the faucet.
When water is being purified by reverse osmosis, it will, in addition to producing purified water, produce a considerable amount of waste water as is well known. This production of waste water, which is a by-product of the reverse osmosis process, and which is also called concentrate water or reject water, has caused concern over the use of the reverse osmosis water purification technology wherever the supply of water to be purified is limited for whatever reason. For example, the ratio of concentrate or reject water to purified water can range from about 3:1 to about 15:1 depending on the particular system. This means that for every gallon of purified water produced, from 3 to 15 gallons is considered as concentrate water and customarily sent to a drain. This waste of water is of great concern particularly in drought areas of the world where water is a particularly precious commodity.
In Hall, U.S. Pat. No. 4,626,346, there is disclosed a reverse osmosis water purification system useful in limited water supply installations such as is found in recreational vehicles, boats and the like which use an unpressurized supply tank for the water source. According to the Hall patent, waste water from the reverse osmosis unit is recycled back to the supply tank to conserve water.